1. Field of the Invention
The invention relates to a control system for a hydroelastic deep-drawing device including a ram, a plurality of hydraulic working cylinders, a plurality of spacer pins extending from selected ones of the working cylinders, and a sheet-holding plate which is supported by the spacer pins and which is movable downwardly with the ram. The deep-drawing device of this type also includes a drawing punch which is movably guided in a drawing direction of the device and which is acted on by a hydraulic medium, and a hydraulic drawing apparatus which is provided with multi-point energizing in accordance with a shaped geometry of the workpiece, the hydraulic drawing apparatus having a plurality of hydraulic control circuits, each of which activates at least one of the drawing punch and the sheet-holding plate in accordance with an effective zone of the workpiece and an effective zone of the sheet-holding plate and through which the drawing apparatus is selectively energizeable.
2. discussion of the Related Art
German Patent Application DE-P-4,008,377.2, relates to a hydroelastic deep-drawing device in presses for drawing shaped sheet-metal parts, having a sheet-holding plate supported by the tool relative to hydraulic pressure cylinders and via spacing pins. A punch is movably guided in the drawing direction and is supported on at least one piston which is guided in a cylinder and can be acted upon by hydraulic medium. This application realizes computer-assisted hydroelastic deep drawing having process capability, in which the pressure cylinders are arranged according to the hole pattern and the spacing pins are supported on the pressure cylinders for the effective zone of the sheet-holding plate, and the effective zone of the drawing punch can be activated in accordance with the shaped geometry of the workpiece.
This process is achieved by the fact that:
a) a hydraulic drawing apparatus is provided with multipoint energizing in accordance with the shaped geometry of the workpiece, in which drawing apparatus a pressure cylinder having an attachable spacing pin is allocated to each aiming point, in which arrangement a plurality of hydraulic control circuits can be connected to each pressure cylinder by rotating its cylinder shell,
b) the drawing punch and/or the sheet-holding plate, via the spacing pins put onto the pressure-cylinder pistons, can be activated by one hydraulic control circuit each in accordance with the existing effective zone of the workpiece and the effective zone of the sheet-holding plate, and
c) at least one differential-cylinder piston rod of the drawing punch and/or at least two differential-cylinder piston rods of the sheet-holding plate can be activated in main-cylinder guide circuits for hydraulically energizing the sheet-holding plate and the drawing punch, and, with regard to acceleration travel and braking travel as well as controlled displacement positions, each displacement position can be controlled by means of an external displacement-measuring system according to tool requirement.
With the invention according to this application, it has in particular been possible to reproduce the process advantage of an elastomeric sheet-holder drawing-cushion system, but with the advantage and the possibility of computer-assisted process control. This configuration enables a multiplicity of hydraulic cylinders to be activated in the most restricted space with process capability and computer assistance, i.e. in an identically repeatable manner during the same program, without having to provide each individual cylinder with separately energized valves.
In conventional deep-drawing forming technology, the sheet-holding plate rests on the drawing pins, which are in turn supported on a standardized central drawing-cushion plate. The drawing-cushion plate is in turn supported pneumatically or hydraulically. At high ram velocities, in particular in mechanical presses, a having impact velocities in the region of 300 mm/sec and a heavy weight of the sheet-holding plate in the region of 1 to 15 tons, the mass impact shock on the sheet to be deep drawn is so severe that impact marks occur which then become partly visible later on the formed parts. Furthermore, the surface texture of the lubricating film applied to the sheet to be deep drawn is changed in an uncontrolled manner by the impact shock, or is at least partially pushed away at critical locations, so that controlled operation of the process is no longer possible.
In this respect, it has been proposed to control more precisely the plunging of sheet-holding plates, by synchronously pre-accelerating each sheet holding plate from its stationary position (V=0) over the plunging stroke to the ram velocity, so that the mass impact shock can be reduced to the greatest possible extent towards zero. However, there is no solution for this with regard to the control system for a deep-drawing system or for a correspondingly advantageous device.